Elastomeric materials reinforced with arrays of parallel layers juxtaposed to achieve increased tensile strength are well known in the art.
Power transmission belts as described in U.S. Pat. No. 5,244,436 to Kurokawa being an example. This patent discloses a v-belt comprising a plurality of longitudinally extending load-carrying cords embedded in an adhesive rubber layer; a compressing section having a plurality of laterally extending cords embedded in a second rubber layer; and a reinforcing rubber layer interposed between said layers to maintain a space between and thereby prevent inadvertent contact between laterally extending cords and load-carrying cords.
Other products such as conveyor belts, tires and hoses are similarly cord reinforced.
U.S. Pat. No. 3,607,592 discloses a portable rubber platform having a ply of rubberized steel cord 3 and 6 spaced by a layer of transverse textile members to achieve a one-way longitudinal rigidity. That invention related to portable platforms suitable for use as, for example, temporary bridges, catwalks and other walkways, and temporary roads on unfirm ground or swamps.
According to that invention a portable platform comprised a flexible composition having embedded therein a composite reinforcement comprising a textile reinforcement together with at least two layers of individually flexible transverse substantially inextensible metal cords, the metal cords in each layer lying substantially parallel with each other and substantially at right angles to the length of the platform, the separation of the transverse metal-cord layers being sufficient to confer a substantial degree of transverse rigidity upon the platform as a whole, and an interposed textile constituent of the composite reinforcement being disposed between each transverse metal-cord layer and the adjoining transverse metal-cord layer.
According to one aspect of that invention, a portable platform as described above had a composite reinforcement including a layer of longitudinal substantially inextensible metal cords lying substantially parallel with each other and with the length of the platform, said layer of longitudinal metal cords being disposed between an interposed textile constituent of the composite reinforcement and the layer of transverse metal cords which lies closest to the load-bearing surface of the platform.
The longitudinal metal cords were either continuous or discontinuous. When they are discontinuous they may be in parallel, overlapping relationship with each other. The discontinuous metal cords may be of any convenient lengths.
Usually the metal cords are steel cords. The steel cords preferably had a percentage extensibility of less than 5 percent. Suitable cords are composed of intertwisted strands of steel wire; for example, the cords may be composed of from six to 24 strands of steel wire of about 0.001 to 0.010 inch diameter. The cords were normally arranged in close side-by-side relationship and may suitably be arranged at a density of from eight to 24 cords per inch.
Preferably the composite reinforcement consisted of two layers of transverse steel cords with a single layer of textile reinforcement between them and a layer of longitudinal steel cords disposed between the textile layer and the layer of transverse steel cords which lies closer to the load-bearing surface of the platform.
This prior art invention provided a portable platform which can be erected simply by applying moderate tension e.g. about 50-80 pounds per inch from supports at the ends. The platform has remarkable transverse rigidity, so that sagging of the edges does not occur to any undesirable extent when a person or vehicle stands on or moves along the platform with weight acting at the edges of the platform, and so that twisting of the platform is limited. The platform could be rolled up and transported in convenient rolls.
In addition, the layer of longitudinal metal cords above the textile reinforcement gives longitudinal rigidity with respect to loads acting down upon the load-bearing surface of the platform.
Continuous longitudinal metal cords also added to the tensile strength of the platform whereas when discontinuous longitudinal metal cords were used, though they give longitudinal rigidity to the platform, the tensile strength is then provided solely by the textile reinforcement. Because of the substantially inextensible nature of the metal cords longitudinal sagging cannot occur even when the metal cords are discontinuous unless the textile reinforcement below the discontinuous longitudinal metal cords stretches appreciably which requires considerable force. Nevertheless the platform may be easily rolled up with the load-bearing surface outermost in the roll because bending of the platform in this direction merely requires circumferential compression of the textile reinforcement below the inextensible metal cords.
The present invention described herein has discovered a novel and useful way of creating a composite structure having a difference in bending stiffness created by a change in modulus between two spaced distinct arrays of parallel cords or by a change in the percent elongation of the cords.